1. Field of the Invention
The present invention relates to a segmented, flexible drill pipe having an improved dovetail configuration for the interlocking segments.
2. Prior Art
In drilling deviated well bores it is necessary to use drill pipe that can bend through the curve of deviation from the vertical. There have been a number of proposals for segmenting regular drill pipe to make the pipe bend without permanently distorting the pipe. For example, U.S. Pat. No. 2,515,366, issued to John A. Zublin, teaches forming a plurality of generally circumferential slots, each cut through the wall of a tubular drill pipe, so that the pipe is divided into a plurality of sections.
While the slots are generally circumferential, they deviate from a true circumference to form a plurality of interengaging and loosely interlocking teeth having a dovetail configuration. The tops and sides of each dovetail, in the Zublin patent, are each relatively straight. This is evident in viewing the drawings accompanying the patent. Further, Zublin's dovetail cuts were vertically true and straight in line with the next.
It has been found that the straight sides of the Zublin dovetail cut allow excessive distortion in bending the drill pipe and often causes damage to the cut if excessive force is applied at the bend. Sometimes, on heavy duty rotation of the drill pipe, the pipe will fail at a particular stress weakened cut. This has been attributed to the vertical alignment, as well as the straight sides of the cuts.
Therefore, it is an object of the present invention to provide an improved dovetail cut for flexible drill pipe.
It is a further object to provide increased rotational strength in the drill pipe having the new dovetail cut.
Another object is to provide improved bending of the flexible drill pipe while retaining integrity of the dovetail teeth.
Yet another object is to provide improved rotational strength of the drill pipe by providing a left hand offset to each succeeding dovetail cut.